Add Matrix to imports since igraph now suggests it

 - Per request of Prof. Brian Ripley
Fix nodesplit summary plot comparison labels

 - They were reversed compared to the ANOHE and relative.effect forest plots
Update NEWS
Add regression test
Add check-as-cran target to Makefile
Fix overfull hbox
Fix BUGSTMP
Update NEWS/DESCRIPTION for 0.5-1
Eliminate use of Matrix (hopefully)